FIGS. 6 and 7 show an example of the multiplex communication device by a prior art spread spectrum communication system executing high speed data communication.
FIG. 6 indicates the construction of a transmitter, in which reference numeral 1 is a serial-parallel converting device; 2-1 .about. 2-n are multiplies; 3-1 .about. 3-n are PN code generators; 4-1 .about. 4-n are BPSK modulators; and 5 is an adder.
In the transmitter described above, inputted high sped data a.sub.1 are converted into parallel data b.sub.1, b.sub.2, . . . , b.sub.n by the serial-parallel converting device 1. Each of the parallel data sets b.sub.1, b.sub.2, . . . , b.sub.n is inputted in one input of each of the multipliers 2-1, 2-2, . . . , 2-n. On the other hand, each of PN codes c.sub.1, c.sub.2, . . . , c.sub.n different from each other outputted by each of the PN code generators 3-1, 3-2, . . . , 3-n is inputted in the other input of each of the multipliers 2-1, 2-2, . . . , 2-n. Outputs d.sub.1, d.sub.2, . . . , d.sub.n of the multipliers 2-1, 2-2, . . . , 2-n are inputted in the BPSK modulators 4-1, 4-2, . . . , 4-n, respectively, to modulate an RF carrier signal e.sub.5. In this way, RF signals f.sub.1, f.sub.2, . . . , f.sub.n are outputted by the BPSK modulators 4-1, 4-2, . . . , 4-n, respectively, which RF signals are inputted in the adder 5. An n-multiplexed spread spectrum signal g is outputted by the adder 5 to be transmitted.
FIG. 7 indicates the construction of the receiver, in which 7-1 .about. 7-n are convolvers; 8-1 .about. 8-n are multipliers; 9-1 .about. 9-n are PN code generators; 10-1 .about. 10-n are detectors; and 12 is a data demodulator.
In the receiver described above, a received signal i is divided into a plurality of signals, each of which is inputted in one input of each of the convolvers 7-1, 7-2, . . . , 7-n.
On the other hand, the PN code j.sub.1, j.sub.2, . . . j.sub.n outputted by each of the PN code generator 9-1, 9-2, . . . 9-n is applied to one input of each of the multipliers 8-1, 8-2, . . . , 8-n. An RF carrier signal m is inputted in the other inputs of the multipliers 8-1, 8-2, . . . , 8-n. The output k.sub.1, k.sub.2, . . . , k.sub.n of each of the multipliers 8-1, 8-2, . . . , 8-n is applied to the other input of each of the convolvers 7-1, 7-2, . . . , 7-n.
The output l.sub.1, l.sub.2, . . . , l.sub.n of the convolvers are inputted in the detectors 10-1, 10-2, . . . , 10-n, respectively. At this time, in the outputs of the convolvers correlation spikes are produced with a same timing for different data channels. The outputs o.sub.1, o.sub.2, . . . , o.sub.n of the detectors 10-1, 10-2, . . . , 10-n are inputted in the data demodulator 12. Demodulated data p are outputted by the data demodulator 12.
The prior art multiplex communication device described above has drawbacks that it is necessary to synchronize the carriers and that a plurality of convolvers (or matched filters) serving as correlators are required.